Structure for absorbing energy

ABSTRACT

A structure for absorbing energy from impacts thereon, the structure being plastically deformable by an impact, with, if appropriate, the possibility that it is at least to some extent disrupted. The structure can include a) ribs for reinforcement, the ribs arranged with respect to one another at an angle with respect to the axial direction such that on failure of a rib a force acting on the structure is immediately absorbed axially by another rib, b) ribs running axially, the ribs being in essence corrugated or of zigzag shape, c) at least one rib running axially in a first plane and connected to at least two ribs running axially in a second plane rotated with respect to the first plane. The structure includes, in the direction of impact, at least two layers, each of which has different compressibility properties and different failure properties.

The invention relates to a structure for absorbing energy from impactsthereon, where the structure is plastically deformable by an impact,with, if appropriate, the possibility that it is at least to some extentdisrupted.

Structures for absorbing energy from impacts thereon are used by way ofexample as what are known as crash absorbers in motor vehicles. Theinstalled location of these is generally between the vehicle fpistoneand a bumper crossmember. During an impact, the crash absorbers deformand thus irreversibly absorb energy. Absorption of the energy bydisruption of the structure of the crash absorbers can avoid high-costrepairs to structurally important parts of the vehicle, as long as theamounts of energy to be absorbed are only relatively small.

The usual structures used as crash absorbers in vehicles, to absorbenergy, are crash boxes composed of steel. Their structure is by way ofexample as described in EP-A 1 477 371, and is deformed on impact.

However, in the search for fuel saving it is desirable to design vehiclecomponents with low weight. For this reason, alternative materials whoseweight is lower than that of steel are also desired for crash boxes. Byway of example, WO-A 2007/147996 discloses that crash absorbers can bemanufactured from a plastic. The usual method here uses afiber-reinforced plastic. The absorber structure disclosed comprises twomembers reinforced with ribs and connected to one another via a plate.Reinforcement here is provided by transverse ribs in the member, andbetween each two transverse ribs there is a cross-rib structure.

However, a disadvantage of this type of structure is that axial impactproduces stepwise absorption, where in each case energy input causesfracture until the next transverse rib is reached, and then energy inputis again needed until again sufficient energy has been introduced todisrupt the structure as far as the next transverse rib. This methodcannot therefore give controlled or controllable failure of the member.

Particularly suitable components for absorbing relatively large amountsof energy are continuous-fiber-reinforced components, but these arerelatively expensive to produce.

In contrast to these, short-glassfiber-reinforced plastics are generallyused only as secondary elements with relatively short installed lengths.These are generally designed as combined cylindrical dome structures, orare designed in similar ribbed form, and are also designed only withrelatively short installed length, because of the risk of buckling.

It is an object of the present invention to provide a structure whichcan absorb the energy from impacts thereon and which has beenmanufactured from a polymer material, where the structure has beendesigned in such a way that it can provide a uniform rate of absorptionof force, through a controllable and controlled failure process.

The object is achieved via a structure for absorbing energy from impactsthereon, where the structure is plastically deformable by an impact,with, if appropriate, the possibility that it is at least to some extentdisrupted, wherein at least one of the following features has beenprovided:

-   a) the structure has ribs for reinforcement, where the ribs have    been arranged with respect to one another at an angle with respect    to the axial direction in such a way that on failure of a rib a    force acting on the structure is immediately absorbed axially by    another rib,-   b) the structure has ribs running axially, the ribs being in essence    corrugated or of zigzag shape,-   c) the structure has at least one rib running axially in a first    plane and connected to at least two ribs running axially in a second    plane rotated with respect to the first plane,-   d) the structure comprises, in the direction of impact, at least two    layers, each of which has different compressibility properties and    different failure properties.

For the purposes of the present invention, an axial direction is, in thecase of an undeformed structure for the absorption of energy, the maindirection of action of an impact affecting the structure. This directionis also generally identical with the greatest longitudinal dimension ofthe structure.

If the structure has ribs arranged at an angle with respect to the axialdirection in such a way that on failure of a rib a force acting on thestructure is immediately absorbed axially by another rib, the ribs havepreferably been rotated at an angle in the range from 10 to 80°,preferably in the range from 45 to 75°, with respect to the axialdirection. This makes it possible that, when a force acts axially on thestructure, one rib first absorbs a portion of the force until it fails,e.g. through fracture, but at the juncture at which failure of the riboccurs the force acting on the structure can immediately be absorbed bythe next rib. The arrangement of the ribs here is such that any crosssection perpendicular to the axial direction always intersects at leasttwo ribs.

In addition to the ribs rotated at an angle with respect to the axialdirection, there can also be longitudinal ribs provided, runningaxially. Longitudinal ribs of this type have usually been provided atleast at the external sides, in a longitudinal direction.

The fact that the force acting on the structure is already acting on afurther rib while the preceding, failing, rib is still at least to someextent in existence can eliminate peaks in the force acting on thestructure. The result is a uniform rate of absorption of the forceacting on the structure.

Correspondingly, the corrugated or zigzag ribs running axially also leadto a uniform rate of failure of the structure. Ribs running axially andthus in the direction of the impact are generally subjected to purelyaxial load. The failure profile of these ribs corresponds to Eulerbuckling, where lateral failure takes place when a critical load isexceeded. This type of design also leads to an undesired sudden changein the force curve. This type of characteristic can be avoided by meansof the corrugated shape. This is attributable to the fact that each ofthe corrugated ribs undergoes further deformation at the top of itscorrugations and finally fails and fractures at the top of thecorrugation. As soon as the ribs fracture at the top of the corrugation,the force immediately acts on the next oblique portion of the corrugatedrib. It is particularly preferable that the corrugated ribs have beendesigned with a radius at their respective corners where their directionchanges. The ribs initially deform at this radius, prior to controlledfailure. Zigzag ribs always fracture at the angles. The force acting onthe ribs is smaller than in the case of a shape designed with a radius.

By virtue of the radius, even a low level of force induces a controlledflexural load on the ribs. Although this reduces the maximum force thatthe rib can absorb before failure, it also reduces the high variation inthe force curve plotted against time.

If the structure for absorbing energy is subject to an axial impact, forexample in the event of an axial crash in a motor vehicle, acharacteristic feature is that asymmetries arising produce not only thedominant axial force but also transverse forces. For this reason it isnecessary that a structure in essence acting axially to absorb energyalso has a certain robustness with respect to transverse forces, inorder to provide reliable functioning even when subject to non-idealstresses.

Such non-ideal stresses occur in particular in motor vehicles by way ofexample if a crash is not directly axial but, for example, occurs withslight displacement or at a slight angle.

An example of a method of raising robustness with respect to transverseforces acting on the structure is to give the structure at least one ribwhich runs axially in a first plane and has connection to at least tworibs running axially in a second plane, rotated with respect to thefirst plane, by way of example, the structure here takes the form of adouble-T member. The ribs running in a first plane and the ribs runningin a second plane, rotated with respect to the first plane, give thestructure particular reinforcement with respect to such transverseforces.

It is by way of example also possible that, in addition to one ribrunning axially in a first plane, and two ribs running axially in asecond plane, rotated with respect to the first plane, as is the case byway of example in a double-T member, there can be two parallel ribsprovided in the first plane, each of which has connection to two ribsrunning axially in a second plane, rotated with respect to the firstplane. All other forms are also possible. By way of example, it is alsopossible to use more than two ribs in each direction.

By virtue of the structure comprising at least two layers in thedirection of impact, each layer having different compressibilityproperties and different failure behavior, it is possible that by way ofexample one layer first fails at a relatively low force level, and thenthat one layer fails at a somewhat higher force level. In the case ofmore than two layers, it is preferable that each layer fails at asomewhat higher force level than the preceding layer. This leads tocontrolled absorption of the force acting on the structure as a resultof the impact, where the force needed to cause failure of a layerbecomes ever greater and the result of this is that the rate at whichthe structure is compressed as a result of failure decreases as thelength is progressively reduced by the failure. The result of this byway of example in the case of a crash in a motor vehicle is a continuousdecrease in the speed of movement of the motor vehicle.

In one preferred embodiment, the ribs have been designed with axiallyincreasing height. It is preferable here that the height of the ribsincreases in the direction of their fastening point and thus in thedirection of impact in the case of an impact acting axially. Theincrease in the height of the ribs is a response to the distribution ofbending moment arising from transverse forces. For example, the bendingmoment of the side facing away from the side on which the impact acts isgreater than directly at the point of action of the impact. It is alsopossible, as an alternative, that the width of the profile increaseswhile the height of the ribs remains the same. Again, this is a responseto the distribution of bending moment when transverse forces arepresent. In another alternative, the dimensions of the structureincrease axially. If the dimensions of the structure increase in anaxial direction, the dimensions increase not only in terms of height butalso in terms of width. Another alternative possibility is that the wallthickness of the ribs increases in an axial direction, the ribs on theside facing toward the point of action of the impact having the lowestwall thickness. It is also possible to realize any desired combinationof the geometry changes described above, i.e. the increase in the heightof the ribs, the increase in the width of the profile, the increase inthe dimensions of the structure in an axial direction, and the increaseof the wall thickness of the ribs.

If the structure has at least one rib running axially in a first planeand connected to at least two ribs running axially in a second plane,rotated with respect to the first plane, another possible design,alongside the design in the form of a double-T member, is by way ofexample a design in which the structure comprises at least two ribsrunning axially in mutually parallel planes, each connected to two ribsrunning in a plane rotated with respect thereto. The ribs running in twoparallel planes here can run directly parallel or have displacementssuch that these ribs running in mutually parallel planes have beenconnected at different sides to a rib running in the plane rotated withrespect thereto. By way of example, it is possible here that twoadjacent ribs have connection at the upper side and that two otheradjacent ribs have connection at their lower side through the ribssituated in parallel planes. It is possible here, for example, that inthe case of three parallel ribs, two ribs have connection at their upperedge to a rib running in a plane situated perpendicularly thereto, andthat the middle rib and the other outer rib of the three parallel ribshave connection at their lower side to the rib running in the rotatedplane. In the case of four parallel ribs, where two have connection attheir upper side, and two at their lower side, to the rib running in aplane rotated with respect thereto, it is possible by way of examplethat the two middle ribs have connection to one another through a ribrunning in another parallel plane situated between the upper and thelower plane. There could moreover by way of example also be other ribsextending from the ribs and running perpendicularly thereto.

Another possibility, alongside parallel ribs connected through the ribsrunning in the plane rotated with respect thereto, is that the ribsconnected to the ribs running in parallel planes run by way of examplein an inclined plane. The angle between the rib running in the firstplane and a rib running in a second plane rotated with respect theretois then by way of example greater than or smaller than 90°.

These cross-sectional forms in which ribs run in at least two planesrotated axially with respect to one another lead in each case to animprovement in the absorption of transverse forces.

The material from which the structure for absorbing energy has beenmanufactured preferably comprises a polymer material. The polymermaterial is by way of example a thermoplastic or a thermoset. These canbe used in filled or unfilled form. However, it is preferable to usefilled polymers.

Examples of suitable polymers are natural and synthetic polymers ortheir derivatives, natural resins, and synthetic resins and theirderivatives, proteins, cellulose derivatives, and the like. These canbe—but do not have to be—materials which cure chemically or physically,for example materials which harden in air, or which cure with radiation,or which cure with heat.

It is possible to use not only homopolymers but also copolymers orpolymer mixtures.

Preferred polymers are ABS (acrylonitrile-butadiene-styrene); ASA(acrylonitrile-styrene-acrylate); acrylated acrylates; alkyd resins;alkylene-vinyl acetates; alkylene-vinyl acetate copolymers, inparticular methylene-vinyl acetate, ethylene-vinyl acetate,butylene-vinyl acetate; alkylene-vinyl chloride copolymers; aminoresins; aldehyde resins and ketone resins; cellulose and cellulosederivatives, in particular hydroxyalkylcellulose, cellulose esters, suchas cellulose acetates, cellulose propionates, cellulose butyrates,carboxyalkylcelluloses, cellulose nitrates; epoxy acrylates; epoxideresins; modified epoxide resins, e.g. bifunctional or polyfunctionalbisphenol A or bisphenol F resins, epoxy-novolak resins, brominatedepoxy resins, cycloaliphatic epoxy resins; aliphatic epoxy resins,glycidic ethers, vinyl ethers, ethylene-acrylic acid copolymers;hydrocarbon resins; MABS (transparent ABS comprising acrylate units);melamine resins; maleic anhydride copolymers; (meth)acrylates; naturalresins; rosins; shellac; phenolic resins; polyesters; polyester resins,such as phenyl ester resins; polysulfones (PSU); polyether sulfones(PESU); polyphenylene sulfone (PPSU); polyamides; polyimides;polyanilines; polypyrroles; polybutylene terephthalate (PBT);polycarbonates (e.g. Makrolon® from Bayer AG); polyester acrylates;polyether acrylates; polyethylene; polyethylenethiophenes; polyethylenenaphthalates; polyethylene terephthalate (PET); polyethyleneterephthalate glycol (PETG); polypropylene; polymethyl methacrylate(PMMA); polyphenylene oxide (PPO); polyoxymethylene (POM); polystyrenes(PS), polytetrafluoroethylene (PTFE); polytetrahydrofuran; polyethers(e.g. polyethylene glycol, polypropylene glycol); polyvinyl compounds,in particular polyvinyl chloride (PVC), PVC copolymers, PVdC, polyvinylacetate, and copolymers of these, and if appropriate partiallyhydrolyzed polyvinyl alcohol, polyvinyl acetals, polyvinyl acetates,polyvinylpyrrolidone, polyvinyl ethers, polyvinyl acrylates andpolyvinyl methacrylates, in solution and in the form of dispersion, andcopolymers of these, polyacrylates and polystyrene copolymers;polystyrene (impact-resistant or non-impact-resistant); polyurethanes,non-crosslinked or crosslinked with isocyanates; polyurethane acrylates;styrene-acrylonitrile (SAN), styrene-acrylic copolymers;styrene-butadiene block copolymers (e.g. Styroflex® or Styrolux® fromBASF SE, K-Resin™ from TPC); proteins, e.g. casein; SIS; triacin resin,bismaleimide-triacin resin (BT), cyanate ester resin (CE), allylatedpolyphenylene ether (APPE). Mixtures of two or more polymers can also beused.

Polymers particularly preferred are acrylates, acrylate resins,cellulose derivatives, methacrylates, methacrylate resins, melamine andamino resins, polyalkylenes, polyimides, epoxy resins, modified epoxyresins, e.g. bifunctional or polyfunctional bisphenol A resins orbifunctional or polyfunctional bisphenol F resins, epoxy-novolac resins,brominated epoxy resins, cycloaliphatic epoxy resins, aliphatic epoxyresins, glycidic ethers, cyanate esters, vinyl ethers, phenolic resins,polyimides, melamine resins and amino resins, polyurethanes, polyesters,polyvinyl acetals, polyvinyl acetates, polystyrenes, polystyrenecopolymers, polystyrene-acrylates, styrene-butadiene block copolymers,styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene,acrylonitrile-styrene-acrylate, polyoxymethylene, polysulfones,polyether sulfones, polyphenylene sulfone, polybutylene terephthalate,polycarbonates, alkylene-vinyl acetates and vinyl chloride copolymers,polyamides, cellulose derivatives and copolymers of these, and mixturesof two or more of these polymers.

Polymers particularly preferred are polyamides, such as nylon-4,6,nylon-6, nylon-11, nylon-6,6, nylon-6/6, nylon-6/10, or nylon-6/12,polypropylene, polyethylene, styrene-acrylonitrile copolymers,acrylonitrile-butadiene-styrene, acrylonitrile-styrene-acrylate,polyoxymethylene, polysulfones, polyether sulfones, polyphenylenesulfones, polybutylene terephthalate, polycarbonates, and mixtures ofthese.

The polymer material is preferably a reinforced material. In particular,the polymer material is fiber-reinforced. Any known fibersconventionally used for reinforcement and known to the person skilled inthe art can be used for this reinforcement. Examples of suitable fibersare glass fibers, carbon fibers, apistonid fibers, boron fibers, metalfibers, and potassium titanate fibers. The fibers can be used in theform of short fibers or of long fibers. The fibers can also be presentin ordered or unordered form in the polymer material. In particular whenlong fibers are used, however, an ordered arrangement is usual. Thefibers here can by way of example be used in the form of individualfibers, fiber strands, mats, wovens, knits, or rovings. If the fibersare used in the form of long fibers, or as rovings or as fiber mat, thefibers are usually placed in a mold, the polymer material then beingpoured around them. The resultant structure can have one or more layers.In the case of a structure having more than one layer, the fibers ofeach of the individual layers can have the same orientation, or thefibers of the individual layers can be at an angle of from −90° to +90°to one another.

However, it is preferable to use short fibers. When short fibers areused, these are usually admixed with the polymer composition prior tohardening. The main body of the structure can by way of example bemanufactured via extrusion, injection molding, or casting. It ispreferable that the main body of the structure is manufactured byinjection molding or casting. The short fibers are generally inunoriented form in the structure. However, if the structure is producedvia an injection-molding process, orientation of the short fibers canresult when the polymer composition comprising the fibers is forcedthrough an injection nozzle into the mold.

Suitable reinforcing agents are not only fibers but also any desiredother fillers which are known to the person skilled in the art and whichact to increase stiffness and/or to increase strength. Among these areinter alia any desired particles with no preferential orientation.Particles of this type are generally spherical, lamellar, orcylindrical. The actual shape of the particles here can deviate from theidealized shape. In particular, therefore, spherical particles canactually by way of example also have a droplet shape or a flattenedshape.

Examples of reinforcing materials used, besides fibers, are graphite,chalk, talc and nanoscale fillers.

However, it is particularly preferable to use glass fibers forreinforcement. Glassfiber-reinforced polyamides are particularlypreferred as material for production of the structure for absorbingenergy.

Production of the structure for absorbing energy can use not onlypolymer materials but also metals, which can be shaped via castingprocesses. Suitable materials are therefore by way of examplelow-density metals that are processible via diecasting processes,examples being aluminum and magnesium. However, it is also possible touse ferrous metals, such as steel or cast iron, where these can beprocessed via casting processes.

So that the impact acting on the structure is introduced at a uniformrate, it is preferable that, on the side on which the impact acts uponthe structure there is a piston which at least covers the cross sectionof the structure. However, the cross-sectional area of the piston canalso by way of example be greater than the cross section of thestructure. This piston is preferably manufactured from a stiff material,so that a force acting on the piston at any desired position isuniformly distributed over the structure for absorbing energy. Examplesof suitable materials from which the piston has been manufactured arethe same as the materials also suitable for production of the structurefor absorbing energy. The piston here can have been manufactured frommaterial which is the same as that used for the structure, or else frommaterial differing from the material of the structure.

As a function of the cross-sectional area of the structure for absorbingenergy, the piston can assume any desired cross section. It ispreferable, however, that the piston takes the form of a parallelepiped,cylinder, or prism, with any desired cross section. However, the crosssection can remain constant in an axial direction or else thecross-sectional area of the piston can by way of example increase ordecrease in an axial direction. It is therefore also possible, forexample, that the piston takes the form of a frustum of a cone or of apypistonid.

In particular, the material used to manufacture the piston is the sameas that used to manufacture the structure for absorbing energy.

The arrangement can have the piston at various positions in thecomponent. It is therefore possible by way of example that thearrangement is such that the piston does not act as a piston until acertain load has arisen. To this end, by way of example, there is adeformable-structure region in an axial direction not only in front ofthe piston but also behind the piston. However, the general situation isthat, in the arrangement, the structure absorbing energy is present onlyon that side of the piston facing away from the side on which the impactacts. Although the piston and the structure for absorbing energyrepresent two separate components, it is possible—in particular when thesame material is used—that both components are produced together in asingle shot in an injection-molding process.

The drawings show embodiments of the invention and are explained in moredetail in the description which follows.

FIG. 1 shows a plan view of a diagpiston of a first embodiment of astructure for absorbing impacts.

FIG. 2 shows a plan view of a diagpiston of a second embodiment of astructure for absorbing impacts.

FIG. 3 shows a three-dimensional representation of a first embodiment ofa structure for absorbing impacts with ribs which run in planes rotatedwith respect to one another.

FIG. 4 shows a three-dimensional representation of a structure forabsorbing impacts with ribs running in planes rotated with respect toone another, with increasing rib height.

FIG. 5 shows a three-dimensional representation of a structure forabsorbing impacts with ribs running in planes rotated with respect toone another, with increasing rib width.

FIGS. 6.1 to 6.4 respectively show a cross section of variousembodiments with ribs running in planes rotated with respect to oneanother.

FIG. 7 shows a plan view of a diagpiston of a structure with threelayers and different compressibility properties.

FIG. 8 shows a side view of a structure of the invention, with piston.

FIG. 1 shows a plan view of a diagpiston of a first embodiment of astructure for absorbing impacts.

A structure 1 designed according to the invention for absorbing energyfrom impacts thereon comprises longitudinal ribs 3. The longitudinalribs 3 have axial orientation, and axial direction here corresponds tothe main direction of action of an impact. The arrow 5 shows thedirection of the impact acting on the structure 1. In order to achieve auniform rate of absorption of energy from the impact, the longitudinalribs 3 have been connected to transverse ribs 7. The transverse ribs 7here run at an angle α with respect to the longitudinal ribs 3, theangle being smaller than 90°. The angle α is preferably selected in sucha way that a plane perpendicular to the direction 5 of impact alwaysintersects at least two transverse ribs 7. When one rib fails,therefore, the force acting thereon and due to the impact 5 immediatelyacts on the rib which follows the rib that is failing. A uniform rate ofabsorption of energy is thus achieved.

On the side opposite to the side on which the impact 5 acts, there isgenerally a support 9 to which the structure has been secured. Thesupport 9 usually runs in a plane perpendicular to the direction 5 ofimpact. However, it is also possible that the support 9 runs in thedirection 5 of impact or at any desired other angle with respectthereto.

FIG. 2 shows a plan view of a second embodiment of a structure forabsorbing impacts.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG.1 in that the transverse ribs 7 run in essence in a plane transverse tothe direction 5 of impact, therefore having been oriented parallel tothe support 9. Two longitudinal ribs 11 run in the direction 5 ofimpact, and respectively form the outer sides of the structure 1. Thestructure 1 shown in FIG. 2 moreover comprises corrugated ribs 13oriented axially. The corrugated structure of the ribs 13 gives these ashape which leads to controlled failure. As a result of the impact 5,the corrugated ribs 13 initially become deformed on the side where theimpact acts. The corrugated rib 13 initially bends in the region of thetop 15 of a corrugation, which is usually in the path of a transverserib 7, and this continues until the bending produces failure throughfracture of the corrugated rib. When fracture occurs, the energy of theimpact 5 immediately acts on the next region of the corrugated rib 13 asfar as the next top 15 of a corrugation. This method likewise achieves auniform rate of failure of the structure through a uniform rate of axialcompression.

FIG. 3 shows a first embodiment of a structure which also absorbstransverse forces acting on the structure 1. In this case, the structure1 has been shown three-dimensionally. Unlike the structures of FIG. 1and FIG. 2, the structure 1 shown in FIG. 3 comprises two outerlongitudinal ribs 11, running axially in a first plane. Axial directionin this case again means the main direction 5 of impact. The structure 1as shown in FIG. 3 comprises not only the longitudinal ribs 11 runningaxially in a first plane but also a rib 15 running axially in a secondplane, rotated with respect to the first plane. The design, and themanner in which the ribs 11 and 15 run gives a cross section in the formof a double-T member. By virtue of the ribs running in planes rotatedwith respect to one another, this member is also stable with respect toflexural stress of the type that can be produced by transverse forces.

The embodiment shown in FIG. 4 differs from the embodiment shown in FIG.3 in that the height h of the longitudinal ribs 11 which laterallydelimit the structure 1 increases from the side of action of the impact5 toward the support 9. The increasing height is a response to thebending moment curve produced by transverse forces.

As an alternative to the embodiment shown in FIG. 4, another possibilityis to design the rib 15 running in the second plane with increasingwidth, while the height h of the longitudinal ribs 11 is constant. Thewidth of the structure 1 thus increases from the side of action of theimpact toward the support 9. Another possibility is to design thestructure 1 not only with increasing width as shown in FIG. 5 but alsowith increasing height of the longitudinal ribs 11, as shown in FIG. 4.This type of design provides stability with respect to transverse forcesacting either from above or below, or else laterally on the structure 1.

FIGS. 6.1 to 6.4 show cross sections of various embodiments with ribsrunning in planes rotated with respect to one another. FIG. 6.1 hereshows a cross section corresponding to the embodiments shown in FIGS. 3to 5. This has two longitudinal ribs 11 connected to a rib 15 running ina second plane rotated with respect to the plane in which thelongitudinal ribs 11 run. The rib 15 running in the second plane herehas been connected to the longitudinal ribs 11 centrally, and thesetherefore have sections protruding above and below the rib 15.

The embodiment shown in FIG. 6.2 differs from the embodiment shown inFIG. 6.1 in that, alongside the delimiting longitudinal ribs 11, otherlongitudinal ribs have been provided which respectively protrude aboveand below the rib 15 running in the second plane and are parallel to thedelimiting longitudinal ribs 11. If, as shown in FIG. 4, thelongitudinal ribs 11 have increasing height h, it is preferable in theembodiment shown in FIG. 6.2 that the longitudinal ribs 3 between thedelimiting longitudinal ribs 11 also have increasing height h. If thestructure has increasing width as shown in FIG. 5, the orientation ofthe longitudinal ribs 3 arranged between the delimiting longitudinalribs 11 is preferably such that the distances between the individuallongitudinal ribs 3 and 11 increase at a uniform rate from the area ofaction of the impact 5 toward the support 9.

Another possibility, alongside a continuous rib 15, is connection, asshown in FIG. 6.3, of the longitudinal ribs 3 and 11 to the ribs 15, 17,and 19 running in planes rotated with respect to the longitudinal ribs 3and 11, where the connection between the ribs 15, 17, and 19 and thelongitudinal ribs 3 and 11 is respectively at a different height. In theembodiment shown in FIG. 6.3, therefore, a first rib 17 running in thesecond plane connects one delimiting longitudinal rib 11 to alongitudinal rib 3 along the underside of the ribs 3 and 11, and one rib15 running in a second plane connects two longitudinal ribs 3 to oneanother, and a third rib 19 connects a longitudinal rib 3 to the seconddelimiting longitudinal rib 11 at the upper side of the ribs 3 and 11.

FIG. 6.4 shows an alternative to the embodiment shown in FIG. 6.3. Inthis embodiment, the delimiting longitudinal ribs 11 do not run in aplane rotated by 90° with respect to the rib 15, 17, and 19, but insteadrun at an angle greater than 90°, the result therefore being atrapezoidal shape. One of the effects of the trapezoidal shape is tofacilitate the demolding of the structure 1 from an injection mold.Additional longitudinal ribs 3 extending above and below the rib 15running in the central plane provide further reinforcement.

Besides the cross-sectional shapes shown in FIGS. 6.1 to 6.4, anydesired other cross section for a rib structure in which ribs 3, 11, 15,17, and 19 run in planes rotated with respect to one another is alsoconceivable.

FIG. 7 shows by way of example a plan view of a diagpiston of astructure with three layers with different compressibility properties.By virtue of the different compressibility properties, the force thathas to act on each of the layers to produce failure of the individuallayers is different. The structure comprises a support 9, to which thestructure has been secured, and an area 21 on which an impact 5 acts. Inthe embodiment shown here, the structure 1 comprises three layers. In afirst layer 23, there is a first rib 25 at an angle α with respect to aplane transverse to the direction 5 of impact. When an impact acts onthe area 21, this moves toward the support 9. This deforms the rib 25until its orientation is parallel to the area 21. It is possible herethat the rib 25 by way of example fractures at a site of connection tothe area 21 or at a site of connection to a second layer 27. Anotherpossibility is that the rib 25 fractures at any desired site betweenthese. In the embodiment shown here, the second layer 27 has beendesigned as a curved profile, in this case a circular profile. Once thefirst layer 23 has failed, the force acts by way of the area 21 on thesecond layer 27. The second layer 27, in this case the circular profile29, is initially deformed by compression until fracture causes it tofail. The circular profile 29 of the second layer 27 is in contact withribs 31 of a third layer 33. The ribs 31 here have been designed in sucha way that the force needed for failure of the ribs 31 is greater thanthe force required for failure of the rib 25 or of the structure 29.This is achieved by way of example as shown in FIG. 7 in that the ribs31 meet at an angle. The ribs 31 thus support one another during actionof an impact in the direction 5 of impact.

However, besides the structure shown in FIG. 7, any other desiredstructure of the layers 23, 27, and 33 where each of the individuallayers 23, 27 and 33 has different compressibility properties is alsoconceivable. Another possibility, therefore, is that differentcompressibility properties are achieved by placing the ribs more closelytogether and thus providing more ribs. The ribs run here by way ofexample as in the embodiments shown in FIG. 1 or 2 or else as inembodiments of FIGS. 3 to 6.4.

FIG. 8 shows a side view of a structure 1 with a piston. The structureshown in FIG. 8 comprises laterally delimiting longitudinal ribs 11,designed with increasing height, as in the embodiment of FIG. 4.However, any desired other structure that accords with the embodimentsof FIGS. 1 to 7 is also possible. The structure 1 has been secured to asupport 9. A piston 35 has been attached on the side on which an impact5 acts on the structure 1. The piston 35 transfers the energy of theimpact 5 at a uniform rate into the structure 1. The piston 35 here isby way of example a solid parallelepiped, or cylinder, or a solid prism,with any desired cross section. Another possibility is that by way ofexample a frustum of a cone or of a pypistonid is used as piston 35. Thepiston 35 has been manufactured from a material which is not deformed byaction of the impact 5. Absorption of energy from the impact takes placeexclusively in the structure 1. The material for the piston 35 is by wayof example the same as the material for the structure 1.

In another possible alternative, the piston 35 is by way of examplemanufactured from a material different from that of the structure 1. Ifthe structure 1 has been manufactured from a plastic, it is possible byway of example to form the piston 35 from a metal or from a cepistonic.However, it is preferable that the same material is used to manufacturethe piston 35 and the structure 1.

The invention claimed is:
 1. A structure for absorbing energy fromimpacts thereon, the structure being plastically deformable by animpact, with a possibility that the structure is at least to some extentdisrupted, the structure comprising: a) first ribs for reinforcement,the first ribs being arranged with respect to one another at an anglewith respect to an axial direction such that, on failure of one of thefirst ribs, a force acting on the structure is immediately absorbedaxially by another of the first ribs; b) second ribs running axially,the second ribs being of corrugated shape or of zigzag shape; and c) atleast one third rib running axially in a first plane and connected to atleast two fourth ribs running axially in a second plane that is rotatedwith respect to the first plane, wherein the first, second, third andfourth ribs are different from each other, or wherein the first, secondand third ribs are different from each other.
 2. The structure accordingto claim 1, wherein the fourth ribs have axially increasing height. 3.The structure according to claim 1, wherein dimensions of the structureincrease axially.
 4. The structure according to claim 1, wherein thethird rib running axially in the first plane is connected to the atleast two fourth ribs running axially in the second plane such that thefourth ribs running axially in the second plane protrude above and belowthe at least one third rib running axially in the first plane.
 5. Thestructure according to claim 1, which comprises at least two third ribsrunning axially in mutually parallel first planes, where the at leasttwo third ribs running in mutually parallel first planes are connectedto, respectively, two fourth ribs running in a second plane rotated withrespect thereto.
 6. The structure according to claim 5, wherein,respectively, two third ribs running in mutually parallel first planesare connected at different sides to a fourth rib running in the secondplane rotated with respect thereto.
 7. The structure according to claim1, manufactured from a polymer material.
 8. The structure according toclaim 7, wherein the polymer material is reinforced.
 9. The structureaccording to claim 8, wherein the polymer material comprises shortfibers for reinforcement.
 10. The structure according to claim 9,wherein the short fibers are glass fibers, carbon fibers, apistonidfibers, boron fibers, metal fibers, or potassium titanate fibers. 11.The structure according to claim 1, wherein, on a side on which theimpact acts on the structure, further comprising a piston that at leastcovers the cross section of the structure.
 12. The structure accordingto claim 11, wherein the piston is a polymer material or a metal. 13.The structure according to claim 12, wherein the piston and thestructure are of a same material.
 14. The structure according to claim11, wherein the piston is a parallelepiped, a cylinder, or a prism. 15.The structure according to claim 1, wherein the structure furthercomprises, in a direction of impact, at least two layers, each of whichhas different compressibility properties and different failureproperties.